Many heavy duty mobile construction vehicles, such as mobile cranes having booms extendable to in excess of 100 feet, are supported on wheels or tracks of 8 to 10 feet lateral spacing. Under such circumstances, it is mandatory for the stability of the unit in manipulating heavy loads to provide outriggers that can be extended to well beyond the vehicle width, frequently to support spacings in excess of 15 or 20 feet. Generally, four outriggers are used, located at the four corners of the vehicle.
In one type of outrigger construction commonly in use, four telescoping beams are supported crosswise to the normal vehicle travel, or the narrow dimension of the vehicle in side-by-side relation with two beams at the front of the vehicle and two beams at the rear of the vehicle. The beams when retracted to the vehicle travel positions extend only to the normal sides of the vehicle. Power cylinders connected between the vehicle body and the beams allow for powered beam movement between the retracted and extended beam positions. There further is located at the free board end of each beam a jack cylinder mounted to move its piston or shaft in a vertical direction. A float pad is secured to the lower end of the jack cylinder shaft and frequently is in excess of two feet in diameter to provide a large support area against the underlying ground. Actuation of each jack cylinder thereby presses its float pad against the ground and lifts the vehicle to the extent required, even to where the tires may be elevated off the ground. The outriggers thereby virtually support the vehicle and any load that is picked up by the vehicle.
Because of the desire to provide the furtherest extension for the float pads crosswise or laterally of the vehicle travel, the jack cylinders nest against the outer edges of the vehicle in the beam retracted positions, thereby allowing for normal clearance between the road and surrounding obstacles. To maintain this clearance, it is necessary to remove each float pad from its jack cylinder shaft for vehicle travel on highways or the like.
Because of the relatively large size and gauge of the float pad, it can be quite heavy, rendering complicated assemble and disassemble procedures somewhat difficult and undesirable. One very attractive feature of these mobile construction vehicles is the mobility of the unit itself accompanied further by the ease for setting up and dismanteling the unit before and after the actual work.
Further, not only must the outrigger components be readily assembled and disassembled for mobile use, but they must be fabricated in such a manner that they are somewhat immune to damage during normal use. In as much as the outriggers support the vehicle plus any load that may be lifted by the work unit, very heavy duty gauges and constructions are employed. For example, it would not be uncommon to use bolts no smaller than 1/2 inch in diameter and further to have lift jack cylinders each with effective lifting capacity in excess of 40 or 50 tons. Moreover, should the inevitable damage occur to any component, it is desirable to provide that it might be readily replaced with a minimum effort.